The present invention pertains to an anchoring device for fastening in a hole formed in concrete construction components.
More particularly, the invention relates to an expansible anchoring fastener which is anchored by impact in a bore hole with an enlarged tapering undercut provided in a support structure.
The anchoring of known fasteners of the type under discussion expanding on impact in a cylindrical hole is carried out by driving an expander pin into an expansible sleeve.
To enable the expander pin to penetrate the narrowing internal bore, the expander pin is formed with a tapering tip and the narrow part of the expansible sleeve has a very slight taper. For anchoring in cylindrical holes such a structure produces an adequate expansion for the bracing of the fastener expanding on impact in the hole.
However, there are cases of application of such fasteners, in which such tensions, although necessary for the anchorage, are undesirable or even disadvantageous. In these cases an effective anchorage can be achieved only by a form fit, i.e. by flaring the bore hole conically at its base. To achieve outward bending of the expansible blades into the conical enlargement, a considerably greater expansion is required than in the case of an anchorage in cylindrical bore holes.
Fasteners that expand on impact are also known in which, to anchor the fastener, an expander pin resting at the base of the bore hole can be driven into an internal bore starting at the insertion end of the expansible anchor. Such fasteners, although having the advantage that they can be equipped both with an internal and an external thread, do not satisfy the safety regulations, because when a withdrawal stress acts on the expansible anchor, the latter is pulled off the expander cone. The less the expansible anchor and the expander pin are braced during the anchoring, the greater is this risk.